Copper converting process with prolonged blowing period

ABSTRACT

In certain copper pyrometallurgical processes, smelting results in a two-layer system comprising an underlying molten coppersulfide, iron-sulfide matte, which often undesirably contains nickel, and an overlying siliceous slag, which ordinarily contains a residue of impurities but usually only a minority of the nickel from the charge to the reverberatory furnace. In accordance with the present invention, the step of converting the matte to molten copper by blowing air through the matte is effected under such conditions that (1) the blowing period is sufficiently prolonged to ensure progress beyond the &#39;&#39;&#39;&#39;blister&#39;&#39;&#39;&#39; to the &#39;&#39;&#39;&#39;worm&#39;&#39;&#39;&#39; stage, in which the molten copper and nickel are highly oxidized, so much of the nickel is present as nickel oxide; (2) molten reverb slag, with high carrying capacity for nickel oxide though not necessarily any free silica, is provided over the molten copper in the converter to absorb the nickel oxide; and (3) the nickel oxide containing slag from the converter is returned to the reverb and from there is scrapped.

Bushaw et al.

United States Patent [191 June 25, 1974 [5 COPPERCONVERTING PROCESS WITH PROLONGED BLOWING PERIOD [75] Inventors: Wayne Bushaw; Adam T. Halliday;

David R. Mukavitz; Richard L. Loan, all of White Pine, Mich.

[73] Assignee: Copper Range Company, New

York, NY.

22 Filed: Nov. 2, 1971 211 App]. No.: 195,001

Related US. Application Data [63] Continuation of Ser. No. 822,144, May 6, 1969,

abandoned.

52 vs. C]. 75/76, 75/75 [51] Int. Cl C22b 15/00 [58] Field of Search 75/74, 75, 73, 76

[56] References Cited UNITED STATES PATENTS 800,130 9/1905 Aiken 2,222,592 1 1/1940 Dobrovolny 2,668,107 2/1954 Gordon et a1.

3,281,236 10/1966 Meissner' 75/73 3,437,475 4/1969 Themelis et al. 75/74 3,56I,9 52 2/1971 Greenberg 75/76 Primary ExaminerL. Dewayne Rutledge Assistant Examiner-W. R. Satterfield Attorney, Agent, or Firm-Morse, Altman, Oates &

Bello [57] ABSTRACT progress beyond the blister to the worm stage, in

which the molten copper and nickel are highly oxidized, so much of the nickel is present as nickel oxide; (2) molten reverb slag, with high carrying capacity for nickel oxide though not necessarily any free silica, is provided over the molten copper in the converter to absorb the nickel oxide; and (3) the nickel oxide containing'slag from the converter is returned to the reverb and from there is scrapped.

4 Claims, 3 Drawing Figures PATENTED Jmi25i974 SMELTING CGNVERTING wUm Y I W G F mm m INCREASING DRIVING FORCE TO FORM AFR, Bru/lb-rnole 0 TEMPERATURE "F COPPER CONVERTING PROCESS WITH PROLONGED BLOWING PERIOD This is a continuation, of application Ser. No. 822144, filed May 6, 1969; now abandoned.

BACKGROUND OF THE INVENTION I The-present invention relatesto metallurgicalprocesses and, more particularly, to the production of copper which has been freed from certain impurities in order to maximize electrical conductivity. Nickel is prominent among the impurities which'are dissolved in solid tough pitch (oxygen-containing) copper and which lower its electrical conductivity. It must be reduced to low concentration, e.g., to less than at least 0.014 percent and preferably to less than 0.010 percent. The present invention teaches how to accomplish this. Much copper is obtained from sulfide ores such as chalcocite-Cu s, covellite-CuS, chalcopyrite-CuFeS bornite-Cu FeS and enargi te-Cu As,Sb )S .v Typically in extracting the copper, the processing steps include: flotation to yield a concentrate containing 20 to 30 percent copper as sulfides and oxides; adding suitable fluxes to the concentrate; smelting in a reverberatory furnace under conditions such that copper sulfide and iron sulfide form an underlying-molten solution called matte, and an overlying slag; transferring the matte to a converter furnace; and converting thematte by reaction with oxygen (air) to produce molten copper, S which passes off as a gas, and iron oxide which floats off into the slag, thereby leaving molten copper for separation and casting, I

Both the concentrate and the added fluxes often contain impurities, notably nickel, which tend to dissolve in the matte and tend to remain asdissolved impurities SUMMARY OF THE INVENTION The primary object of the present invention is to perform the converting step, in a process of the foregoing type, by blowing air through the matteundersuch conditions that: (l) the normal two parts of the converter blow are first completed the first part, the iron blow,

to oxidize the iron sulfide toiron oxide which floats up to form part of the slag and to $0 which goes off as a gas; and the second part, the copper blow, to oxidize the copper sulfide to molten copper and to S0 which goes off as a gas the slag being skimmed off the converter and returned to the reverb furnace at various times; (2) fresh molten reverb slag relatively low in nickelcontent and having adequate carrying capacity for nickel oxide is placed onthe molten copper which is now in the blister copper stage; (3) the blowing period is sufficiently prolonged to ensure progress beyond the blister" to the worm or final worm condition; and (4) the temperature is sufficiently high to ensure that both the copper and theslag are in the liquid state. The prolonged blowing, or overblowing," ensures that, since nickel has a greater affinity for oxygen than copper, the majority of the nickel impurity in the copper is converted'to nickel oxide. The liquid state of the slag, and its carrying capacity for nickel oxide even though it may contain no free silica, results in the nickel oxide dissolving in the slag and its removal from BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of the nature and objects of the present invention, reference is made to the following detailed description, taken in connection with the accompanying drawings, wherein:

FIG. 1 is a flow diagram emphasizing important steps in the process of the present invention;

FIG. 2 illustrates a sequence of cross-sectioned samples of copper, each of which first is withdrawn in the liquid state from the system during the converting step and then is allowed to solidify under standard conditions to exhibit certain physical characteristics that indicate the stage which that sample represents of the extent of progress toward completion of the converting operation; and

FIG. 3 is a graph of certain physical-chemical relationships, upon which the present invention is based.

DETAILED DESCRIPTION A copper refining process, involving certain steps of the present invention, is illustrated in FIG. 1. First a copper sulfide concentrate 10 is produced by flotation from original ore and iron sulfide flux 12, together with limestone, is added to provide a reverberatory furnace charge having desired stoichiometric relationships. Next this charge is smelted in a reverberatory furnace under conditions such that copper sulfide and iron sulfide form an underlying matte 16 and a siliceous slag 18. Sulfide matte 16 is transferred from the reverberatory furnace to the converter furnace where it is converted by reaction with oxygen (air) 22 to oxidize sulfur to'sulfur dioxide 26, which escapes as a gas, and to leave reduced molten copper 24 for separation and casting.

It has been found that the blowing period must be sufficiently prolonged to ensure progress beyond the blister" to the worm or final worm conditions. The sequential stages of the copper during the blowing period are indicated in practice by sequentially removing samples from the molten charge in the converter and allowing them to solidify under standard conditions. Thecharacter of the surface of any such sample provides a visual indication of the stage of converting. FIG. 2 illustrates, in cross section, a sequence of typical solidified samples, removed sequentially from the matte in liquid form as the blowing period is continued from the beginning to the end. In the regal condition, illustrated at 30, Cu S particles, but little or no oxygen, is present in the copper matrix. In the clear condition, illustrated at 32, almost all Cu S particles are gone and the surface is flat or clear. In the blister conditions, illustrated respectively at 34, 36 and 38, Cu O particles are dispersed in the copper and S0 is escaping during solidification to form the blisters. In the initial worm, full worm" and final worm" conditions, illustrated respectively at 40, 42 and 44, Cu O particles are dispersed in the copper and S forms in the interior of the molten sample after a solid crust has formed at the upper surface, the relationships being such that the S0 pressure cracks the crust and extrudes molten copper which solidifies in a worm-like configuration. 1n the "flat copper" and peahole copper" states, still more Cu O particles are dispersed in the matte and ever'lower sulfur concentrations finally result in shrinkage cavities that occur on solidification because solid copper is more dense than molten copper and there is insufficient S0 formation to form microporosity which would counteract the macroshrinkage.

In connection with the foregoing, the following additional considerations are significant. First, because of nickel's greater affinity for oxygen than coppers as indicated above, nickel is oxidized preferentially during the overblowing of the blister Cu. Also, as indicated above, a special slag in the converter during the overblowing acts as a trap, or carrier, for the NiO. The prior art, typified by Redmond, US. Pat. No. 2,895,821, issued July 21, 1959, for Process For Refining Blister Copper, teaches adding solid Si0 (e.g., as sand particles) and maintaining this as a solid slag over the blister copper during the overblowing. But a solid slag does not absorb the molten NiO; moreover it is difficult, costly and inefficient to handle. The present invention employs a molten slag conveniently available in the reverberatory furnace. This slag differs from the Redmond teaching in that it normally contains little or no free SiO i.e., although it contains considerable Si and 0, X-ray diffraction studiesof the solidified slag have shown that the Si and O are tied up as silicates. Free Si0 is an excellent slagging agent in that it reacts with and retains other oxides which it is desired be held in the slag but it contributes high viscosity and high melting point to the slag and it is a feature of this invention that the slag be kept fluid to lower cost of handling and to speed the purifying reaction. A fortunate experimental fact underlying the present invention is that, even though the reverb slag does not contain free SiO in the solid state, it nevertheless has the capacity to hold in the slag the NiO which has been preferentially oxidized during the overblow. This is very important since, to achieve the desired Ni removal from the Cu, the Ni must be removed via the slag. The converter slag cannot economically be scrapped because it contains 4 percent or more Cu as Cu O (or as Cu silicate); moreover the violent blowing action traps some molten Cu in the converter slag. Accordingly the converter slag is returned to the reverberatory furnace where, since it constitutes lessthan 8 percent of the total reverb slag volume, it is appreciably diluted. Moreover, its NiO holding, or carrying, capacity is sufficient to retain most or all of the NiO within the reverb slag while the latter releases much of its entrapped Cu which is recovered in the underlying matte. The Cu-denuded reverberatory slag is periodically tapped from the reverberatory furnace and, with its higher NiO content, is scrapped. To achieve 100 percent IACS conductivity by fire-refining, the Ni must be removed from the system. Prior to the present invention, much of the Ni left the smelter-refiner system in the Cu where it lowers conductivity; with this invention, much of the Ni leaves the smelter-refiner system in the reverb slag where it causes no harm and which is scrapped. The relationships of the thermodynamic driving forces discussed above are shown in FIG. 3.

Oxygen blown through the molten material in the converter reacts with the elements present in the order of their decreasing affinity for oxygen. This affinity can be quantitatively expressed in terms of free energies of formation whereby the more negative the free energy of formation of a compound the greater the affinity. At temperatures at which the converter operates, the affinities of the following elements for oxygen decreases in the order given Cu Thus when matte from the reverberatory furnace (F eS and Cu S) is transferred to the converter and O is blown through it, first essentially all the F eS is oxidized to FeO and S0 and no Ni nor Cu is oxidized; after all the Fe has been oxidized, then the Cu S starts to oxidize during continued blowing. Ni is present only in trace amounts, the Ni content in the matte being only about 0.017 percent by total weight of matte (weight percent). If it were preponderant, it would tend to oxidize before the Cu. Under these conditions and using prior conventional converter practice, the somewhat purified product of the converter, so-called blister copper, typically would have a Ni content of 0.019 0.020 weight percent. Numerically, this might appear to be an increase in Ni content but the matte contains a large amount of Fe and this is slagged off during the first part of the converter blow. Accordingly it is more meaningful to consider the ratio of Ni to Cu during the converter blow. Typically these ratios (wt. Ni: wt.% Cu X 0.001) are:

Prior Converter Practice Converter Practice of Present Invention Matte .261 .261 Blister .200 .130

Thus, reflecting the higher affinity of oxygen for Ni rather than for Cu, both old and new converter practices remove Ni preferentially to Cu; the value of the new practice is that it removes Ni even more preferentially relative to Cu. Thus, starting with a typical 0.017 wt.% Ni in the matte, the following are typical Ni contents in wt. percent.

Prior Con- Converter Practice verter Practice of Present Invention Matte 0.017 0.017 Blister 0.020 0.013 Final refined copper 0.019 0.012 7n IACS of final refined copper 99.2-99.5 100.0-100.4

The improvement of one-half to one percent IACS is virtually the difference between failure and success tion such as electrorefining to achieve 100.0l-percent .JACS:.lsasqqrs aissuith-tbgp ssatinrsafisn i is.

The above charge produces a sidewall" matte and slag gf the following composition:

Matte Slag Cu Fe S FeO SiO A1 CaO MgO ore is utilized and unusually high electrical conductivities in the resulting copper are attained. White Pine ore is too low in Fe and S- to smelt. To correct these deficiencies, pyrite (FeS can be bought and added but chalcopyrite (CuFeS is preferable because of its Cu content. Both pyriteandchalcopyrite often contain damaging amounts of Ni. An important advantage of this invention is the freedom it gives to use many sources of pyrite and/or chalcopyrite virtually independent of their Ni contents. The effects of impurities on the electrical conductivity (EC) of Cu are shown by the following table Typical Concentration (Wt/71 i ShQWMEl YYZ.

, .ical and the electrical conductivity to drop below 100.0 percent.

In order to maintain simplicity in the examples below, the following background information is given separately in regard to smelter operations and reactions.

EXAMPLE I The indicated charge contains:

The matte at 63.0% Cu, 15.6% Fe, and 21.4% S is transferred to the converter. Two basic reactions take place in the converter 2FeS 30 2FeO 280 slag blow Cu S o. 2Cu so, copper blow The oxidation of FeS to FeO and of Cu S to Cu is highly exothermic 2FeS 30 2FeO 380 224,200 cal/mole Cu S 0 2Cu S0 128,990 cal/mole Note that the oxidation of the FeS evolves more heat per mole than the oxidation of Cu S. At 66% Cu matte, the converters can keep ahead of the generation of cold cope which consists of scrap copper, matte skulls, refining slags, flue dust, etc. At 70% Cu matte, cold dope generation must be kept to a minimum, because the converter consumes considerably less cold dope. In fact, at Cu matte, external heat (coal, oil, or natural gas) would be required to keep the converter hot enough to consume even a minimum of cold dope. As the matte grade (%Cu) is increased, the amount of iron in the matte is decreased; thus the amount of heat generated by the oxidation of FeS is decreased. The actual prior procedure involved in the converter cycle was as follows: Put four ladles of matte and two ladles of slag into converter and blow converter until all FeS is oxidized to FeO (approx. 30 minutes). Skim off converter slag (approx. two ladles). Put one to two ladles of matte and one ladle of slag into converter. Blow converter untilall FeS is oxidized toFeO (approx. 20 minutes). Skim off converter slag (approx. two ladles). What remains in the converter is mainly white metal pure Cu S. Blow the converter until all Cu S is oxidized to Cu (approx. 3 V2 hours). Several times during this period, turn the converter out of the stack and cold dope is added (approx. l5 tons per charge). Then transfer the blister copper to the refining furnace (approx. tons from five ladles of matte and 15 tons of cold dope. Three converter charges are required to make one refining furnace charge of 240 tons of copper.

The blister transferred to the refining furnace has the following nominal composition:

, 12.1%.r11;Basset-K015112122.sqassnt Cu 02. Ag/ton S 0, As Fe Pb Ni 17.0 wt. percent limestone H 5.0 wt. percent chalcopyrite concentrate 5.5 wt. percent pyrite. The chemical composition of these charge components 60 The process of EXAMPLE I was performed in accor- Cu Fe S S10, A1 0 CaO MgO W.P. Concentratc 32.0 4.5 8.0 37.0 11.0 2.5 2.0 Chulcopyrite 29.0 34.5 35.5 0.5 0.5 Pyrite 45.0 45.0 3.0 2.0 Limestone 3.0 l .5 53.0 1.0

Pierce Smith 13 foot by 30 foot cylindrical converters equipped with a tuyere line consisting of 40 2 inch pipes. The tuyere line supplied with 14 pound air pressure from a 25,000 CFM blower. In the first slag blow (FeO formation and removal), four ladles of matte and two ladles of slag at 175 cubic feet per ladle were transferred from the reverberatory furnace to the converter, which had bee preheated with fuel oil torches between charges. This mixture was blown for approximately 20 minutes and then slagged off. Two ladles of slag were removed and returned to the reverberatory furnace. In the second slag blow (FeO Formation and Removal), one ladle of matte and one ladle of slag were introduced to the previous converter charge. This charge was blown for approximately 15 minutes and then slagged off. The slag was returned to the reverberatory furnace. Approximately two ladles of slag were removed at this point. In the third or finish blow (S formation and removal), during which sulphur is oxidized, a blow period of approximately 1 /2 hours was required. During this blow period, cold dope was slag which was carried over to the next charge cycle.

EXAMPLE Ill The following procedure exemplifies the present invention. Although all impurities were considered, of prime importance was the reduction of nickel (Ni) in the final product cast. This method involved thinning of the slag prior to the finish of the final stage of converting and allowed the converter to be skimmed clean of slag which contains a high concentration of Ni and other trace impurities. Tests have concluded that matte containing 0.017% Ni processed in this manner will yield a final blister copper at 0.013% Ni or less at the present matte grade. The equipment used in converting included two Pierce Smith 13 foot by 30 foot cylindrical, drum-type converters. The tuyere line consists of 40 2 inch air pipes supplied with l4-pound air pressure at 25,000 CFM for the blowing stages. Copper matte was transferred from the reverberatory furnace at 65 66% copper. The first slag blow (FeO Formation and Removal) involved transfer of the converter charge, consisting of four ladles of copper matte (approximately 100 T) and two ladles of reverb molten slag (approximately 30 T). After charging was complete, the converter was placed in the blow position and the blow" process was continued for 20 minutes. Upon completion of the blow" cycle, the converter was slagged and two ladles were removed and returned to the reverberatory furnace. In the second slag blow (FeO Formation and Removal), one ladle of copper matte and one ladle of molten slag were introduced to the previous charge that remained in the converter. The molten slag was not added until the converter was placed into the blow" position. This charge was blown for approximately 15 minutes, and then one and threefourths to two ladies of slag were skimmed and returned o the s rbsratqr u e 1 he finals! 999-.

per blow (SO; formation and removal). performed to oxidize the sulphur. the duration of this final blow was I to 1% hours. During this blow, cold dope" (refiner furnace slag, transfer hopper skulls, soda slag, transfer ladle skulls, etc.) was introduced to the remaining converter charge. Two or more ladles at cubic feet each of cold dope were introduced between blow stages. The addition of cold dope during this portion of the converter cycle permitted reclamation of inherent copper losses by convenient means. The addition of cold dope tended to cool thecharge and the slag formed was of a heavy molten consistency. Reverberatory molten slag (one ladle) was introduced to the remaining charge when the charge was approximately 5 minutes from finish and at a point when the worm formed on a 3 inch sample cup extends around the complete circumference of the cup. The converter was still in the blow portion of the cycle when the addition of the slag was made. The introduction of reverberatory slag provided two desirable effects: I) It thinned the slag produced during the addition of cold dope. (2) It produced a slag by which a percentage of MO is removed with other trace impurities. After introducing the reverberatory slag, the converter was held in the blow position for approximately 2 minutes and thenslagged clean. The slag was returned to the furnace. The remaining charge in the converter was now blister copper awaiting transfer to one of two refining furnaces for further removal of trace impurities and deoxidizing. I

CONCLUSION The present invention thus provides a novel copper refining process in which nickel is removed from copper matte during converting. The process produces fire-refined copper with a Ni content of less than 0.015 wt. percent and a conductivity of at least 97.5 percent IACS. The Ni is oxidized preferentially to copper by overblowing in the presence of a molten slag having carrying capacity'for the Ni oxide but not necessarily containing any appreciable amount of free silica. Since certain changes may be made in the foregoing disclosure without departing from the invention hereof, it is intended that all matter contained in the above description and shown in the accompanying drawing be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

l. A copper refining process comprising the steps of producing a predominantly copper sulfide concentrate by flotation of ore and adding a member of the class consisting of pyrite and chalcopyrite to provide a reverberatory system under such conditions that copper oxide reacts with iron sulfide to form copper sulfide and iron oxide, forming an underlying matte of said copper sulfide, forming an overlaying slag from said iron oxide and from added silica, and converting said copper sulfide to copper by blowing oxygen through said system under such condition as first to oxidize iron sulfide to iron oxide (which goes into the slag) and S0 (which goes off as a gas), second to oxidize copper sulfide to molten copper and S0 third to dissolve nickel oxide in siliceous reverberatory slag, fourth to prolong the normal blow beyond the blister and full worm" stages so that the nickel impurity will be substantially oxidized preferentially to the copper and so that this 9 nickel oxide will be absorbed into the molten siliceous slag and carried there, thereby permanently. removing a majority of the nickel impurity from the copper, the entire system remaining molten throughout the purification process, said temperature being greater than 2,l50 F. and said blowing period sufficiently prolonged to reduce the content of said nickel to less than 0.015 weight percent, said siliceous slag containing substantially no free silica in the solid state.

2. The copper refining process of claim 1 wherein said blowing period is sufficiently prolonged to increase the electrical conductivity of said copper to in excess of 97.5 percent lACS.

3. The copper refining process of claim 1 wherein said blowing period is sufficiently prolonged to increase copper oxide reacts with iron sulfide to form copper sulfide and iron oxide, forming an underlying matte of said copper sulfide containing nickel impurity, forming an overlying slag from said iron oxide and from added silica, and converting said copper sulfide to copper by blowing oxygen throughsaid system under such condition as first to oxidize iron sulfide to iron oxide, which goes into the slag, and S0 which goes off as a gas, second to oxidize copper sulfide to molten copper and S0 third to add to said systemreverberatory slag, fourth to prolong the normal blow beyond the blister and full worm stages so that said nickel impurity will be substantially oxidized preferentially to the copper and so that said reverberatory nickel impurity will be absorbed into said molten slag and carried there, thereby permanently removing a majority of said nickel impurity from the copper, the entire system remaining molten throughout the purification process, said temperature being greater than 2,l50F. and said blowing period sufficiently prolonged to reduce the content of said nickel to less than 0.015 weight percent, said siliceous slag containing substantially no free silica in the solid state and said blowing period being sufficientlyv prolonged to increase the. electrical conductivity of said copper to in excess of 97.5 percent lACS.

l =l= l 

2. The copper refining process of claim 1 wherein said blowing period is sufficiently prolonged to increase the electrical conductivity of said copper to in excess of 97.5 percent IACS.
 3. The copper refining process of claim 1 wherein said blowing period is sufficiently prolonged to increase the electrical conductivity of said copper to in excess of 100 percent IACS.
 4. A copper refining process comprising the steps of producing a predominantly copper sulfide concentrate by flotation of ore and adding a member of the class consisting of pyrite and chalcopyrite to provide a reverberatory furnace system under such conditions that copper oxide reacts with iron sulfide to form copper sulfide and iron oxide, forming an underlying matte of said copper sulfide containing nickel impurity, forming an overlying slag from said iron oxide and from added silica, and converting said copper sulfide to copper by blowing oxygen through said system under such condition as first to oxidize iron sulfide to iron oxide, which goes into the slag, and SO2, which goes off as a gas, second to oxidize copper sulfide to molten copper and SO2, third to add to said system reverberatory slag, fourth to prolong the normal blow beyond the ''''blister'''' and ''''full worm'''' stages so that said nickel impurity will be substantially oxidized preferentially to the copper and so that said reverberatory nickel impurity will be absorbed into said molten slag and carried there, thereby permanently removing a majority of said nickel impurity from the copper, the entire system remaining molten throughout the purification process, said temperature being greater than 2,150*F. and said blowing period sufficiently prolonged to reduce the content of said nickel to less than 0.015 weight percent, said siliceous slag containing substantially no free silica in the solid state and said blowing period being sufficiently prolonged to increase the electrical conductivity of said copper to in excess of 97.5 percent IACS. 